A novel pyrene-based dual multifunctional fluorescent probe for differential sensing of pH and HSO3− and their bioimaging in live cells

We designed and synthesized a new fluorescent probe for detecting pH and HSO3− using pyrene as an electron donor (D) and pyridine as an electron acceptor (A). The fluorescent probe for sensing pH and HSO3− could distinguish these by their spectral properties in different media. pH titrations indicated that the probe displayed a ratiometric emission (pH 7.10–1.36) with a pKa of 4.26, responded linearly to minor pH fluctuations within the acidic pH range of 3.00–5.50 in CH3CN/H2O (1/3, v/v), and exhibited a remarkable emission enhancement (pH 7.10–13.09) with a pKa of 10.91 and a linear response in the extremely alkaline pH range of 9.75–11.35 in CH3CN/H2O (1/19, v/v). Interestingly, the probe also responded to HSO3− with an obvious turn-off fluorescence signal in PBS buffer (pH = 5.00, 1.5% DMSO). This could be attributed to the Michael addition of HSO3− to the α,β-unsaturated ketone, which resulted in breaking of the conjugation. The detection limit (LOD) of the probe for HSO3− based on the definition by IUPAC was calculated to be 1.9 nM. Furthermore, the probe was employed successfully for the imaging of pH and HSO3− in live cells, which indicated that the probe was a suitable indicator for imaging the distribution of pH or HSO3− and tracking their changes.